The subject matter disclosed herein relates to gamma ray detection, and, more particularly, to a technique for correcting non-linearity in a gamma ray detector.
A wide range of imaging techniques are known and currently in use, particularly for medical diagnostic applications. Certain of these techniques, commonly referred to as nuclear imaging, rely on detection of gamma rays during the radioactive decay of a radioisotope (or radionuclide), commonly administered in the form of a radiopharmaceutical agent that can be carried, and in some cases, bound to particular tissues of interest. A gamma ray detector detects the emissions via a gamma camera that typically includes a collimator, a scintillator, and a series of photomultiplier tubes. The collimator allows only emissions in a particular direction to enter into the scintillator. The scintillator converts the gamma radiation into lower energy ultraviolet photons that impact regions (pixels) of the photomultiplier tubes. These, in turn, generate image data related to the quantity of radiation impacting the individual regions. Image reconstruction techniques, such as backprojection, may then be used to construct images of internal structures of the subject based upon this image data.
One challenge in the use of gamma cameras is that they typically do not have a linear spatial response. Consequently, a calibration process is required to determine a necessary linearity correction for use in processing data collected by the cameras. The calibration process is done both during production of a gamma camera and during gamma camera maintenance. In general, the calibration process may be completed with the use of a linearity phantom, which captures gamma rays passing through its many apertures. The coordinates of the apertures are then used to determine the non-linearity of the gamma camera and generate the appropriate linearity correction map. However, linearity phantoms may be heavy, expensive, difficult to acquire and logistically cumbersome to use. Moreover, such calibration procedures typically require a visit by a skilled technician, and may be done at relatively extended intervals during regular or special system maintenance. Typically, a linearity phantom is placed directly on the detector. Thus, the collimator may need to be removed from the detector prior to the installation of the phantom. Collimator removal and replacement (in contrast to collimator exchange) is a non-standard and cumbersome operation that may require tools and skills beyond the capacity of hospital technicians.